Stars Leighton Meester and Blake Lively were having trouble getting in and out of the very high heels the scene called for. "They needed crew members to help get them on," our on-set spy dished. "The girls also had a lot of trouble walking in them."

Which explains why the two starlets immediately slipped into their Uggs the moment the cameras turned off. Once comfy, Leighton played with her BlackBerry while Blake talked shop with the camera crew and costume designers.

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Lively was overheard asking about a pair of Stuart Weitzman heels that an extra had been wearing a day before. The blond fashionista was upset when she heard they were the actress' own. "Man, I loved them," she sighed. We're sure that Lively, like her character Serena Van Der Woodsen, will find a way to get what she wants!